Method and apparatus for closed-loop ignition time control

Abstract

A closed-loop control of the instant of ignition is proposed, in which, with the aid of an ionic current sensor, the end of the ignition phase of an operational mixture of an internal combustion engine is ascertained as an actual value and the instant of ignition is corrected in accordance with the deviation of this actual value from a set-point value relating to the crankshaft angle. In this manner, the instant of ignition in externally ignited internal combustion engines, or the instant of injection in compression ignition engines, can be optimized by simple means, without expensive adjusting devices for the ignition angle or for the instant of injection. In addition, it is possible with a closed-loop control of this kind to perform an optimal adaptation of the ignition to varying peripheral circumstances such as the thermal status of the engine, characteristics of the fuel and of the combustion air, engine wear, and so forth.

What is claimed and desired to be secured by Letters Patent of the United States is: 
     
       1. A method for controlling the instant of ignition in closed-loop fashion in an internal combustion engine, comprising the steps of: detecting the ionic current released during combustion of the operational mixture at a predetermined distance from the point of ignition in a combustion chamber of the engine, where the flame front reaching said distance has ignited a mixture volume less than 5% of the total volume;   generating an actual value signal from the ionic current, representing the end of the ignition phase of the operational mixture;   generating a set-point value signal before top dead center as a function of crankshaft angle, representing a desired end of the ignition phase of the operational mixture;   comparing the actual value signal to the set-point value signal and generating a difference signal; and   correcting the instant of ignition in the combustion chamber of the engine as a function of the difference signal.   
     
     
       2. The method as defined in claim 1, wherein the phase relationship of the actual value signal and the set-point value signal is compared and the difference signal generated. 
     
     
       3. The method as defined in claim 1, wherein the set-point value signal is adjustable as a function of at least one operational parameter which has an effect on the ignition of the operational mixture. 
     
     
       4. The method as defined in claim 2, wherein the set-point value signal is adjustable as a function of rpm. 
     
     
       5. The method as defined in claim 3, wherein the set-point value signal is adjustable as a function of engine temperature. 
     
     
       6. The method as defined in claim 4, wherein the set-point value signal is adjustable as a function of intake manifold vacuum. 
     
     
       7. The method as defined in claim 3, wherein the set-point value signal is adjustable as a function of the aspirated fuel/air mixture. 
     
     
       8. The method as defined in claim 1, wherein the ionic current is detected at two predetermined distances from the point of ignition in the combustion chamber, and wherein the actual value signal generated is an average of the ionic currents detected at the two locations. 
     
     
       9. The method as defined in claim 1, wherein the ionic current is detected at two predetermined distances from the point of ignition in the combustion chamber and at different times, and wherein the actual value signal is generated from the ionic current subsequently detected. 
     
     
       10. An apparatus for controlling the instant of ignition in closed-loop fashion in an internal combustion engine, comprising: at least one ionic current sensor located at a predetermined distance from the point of ignition in a combustion chamber of the engine, where the flame front reaching said distance has ignited a mixture volume less than 5% of the total volume, and in the path of the ionic current released during combustion of the operational mixture in the combustion chamber, said at lease one ionic current sensor generating a signal representative of the ionic current detected;   a pulse shaper connected to each ionic current sensor for receiving the output signal from each ionic current sensor and generating an actual value signal therefrom representing the end of the ignition phase of the operational mixture;   ignition angle set-point transducer means for generating a set-point value signal before top dead center representing a desired end of the ignition phase of the operational mixture;   a comparator circuit connected to the output of said pulse shaper and said ignition angle set-point transducer means for comparing the phase relationship between the actual value signal and the set-point value signal, and generating a difference signal as an output;   an integrator circuit connected to the comparator circuit for integrating the difference signal; and   an ignition time adjusting device connected to the integrator circuit and being actuated as a function of the difference signal.   
     
     
       11. The apparatus as defined in claim 10, wherein the ignition angle set-point transducer means comprises: a crankshaft angle transducer and a pulse shaper connected thereto and to said comparator circuit. 
     
     
       12. The apparatus as defined in claim 11, wherein the ignition angle set-point transducer means comprises: a crankshaft angle transducer, a pulse shaper connected thereto, and a signal delay circuit connected to the pulse shaper and to the comparator device, said signal delay circuit receiving input signals indicative of various operational parameters affecting the course of combustion for adjusting the set-point value signal received from the pulse shaper as a function of at least one of the operational parameters received. 
     
     
       13. The apparatus as defined in claim 10, wherein said at least one ionic current sensor is disposed in the insulating body of a spark plug. 
     
     
       14. In combination with an internal combustion engine, including at least one main combustion chamber, an associated precombustion chamber and connecting channel connecting the main combustion chamber with the precombustion chamber, an apparatus for controlling the instant of ignition in closed-loop fashion in said associated precombustion chamber, said apparatus comprising: an ionic current sensor located in the connecting channel in the path of the ionic current released during combustion of the operational mixture in the precombustion chamber, and where the flame front has ignited a mixture volume less than 5% of the total volume, said ionic current sensor generating a signal representative of the ionic current detected;   a pulse shaper connected to the ionic current sensor for receiving the output signal therefrom and generating an actual value signal representing the end of the ignition phase of the operational mixture;   ignition angle set-point transducer means for generating a set-point value signal before top dead center representing a desired end of the ignition phase of the operational mixture;   a comparator circuit connected to the output of said pulse shaper and said ignition angle set-point transducer means for comparing the phase relationship between the actual value signal and the set-point value signal, and generating a difference signal as an output;   an integrator circuit connected to the comparator circuit for integrating the difference signal; and   an ignition time adjusting device connected to the integrator circuit and being actuated as a function of the difference signal.   
     
     
       15. The combination as defined in claim 14, further including a glow plug mounted to the precombustion chamber to provide ignition in the precombustion chamber. 
     
     
       16. The combination as defined in claim 14, further including a spark plug mounted to the precombustion chamber to provide ignition in the precombustion chamber. 
     
     
       17. The combination as defined in claim 14, further including a fuel jet injection nozzle which serves the purpose of ignition.